Solid state motor control and power control systems have been known heretofore. While such systems have employed various mounting structures for the various semiconductors in order to electrically connect the same as well as to provide for flow of coolant medium thereabout, such structures have generally been rather complex in nature and limited to use in one type of control system rather than having any universality of application, thus requiring a large number of different parts if such structures are to serve even a limited range of control systems in customary use. For example, one of these known structures is a heat sink module wherein a single semiconductor, a pair of heat sinks and a support are clamped together and are connected to a bus bar and mounted on a wall or a panel such as shown in C. S. Otteson et al U.S. Pat. No. 3,536,960, dated Oct. 27, 1970. Another of these known structures relates to a semiconductor stack wherein a plurality of semiconductor devices, electrodes and heat sinks are stacked within a rectangular frame and held in compression by spring washers and with a number of insulator elements interspersed in suitable places to electrically isolate the semiconductor devices as required such as shown in J. J. Steinmetz et al U.S. Pat. No. 3,523,215, dated Aug. 4, 1970. While these prior known semiconductor device mountings have been useful for their intended purposes, this invention relates to improvements thereover.